The present invention relates to dual-sieve oxygen concentrators normally used by invalids at their home or in nursing home or hospital care; its principal purposes are to achieve more efficient utilization of the sieves and longer freedom from operating problems.
Portable dual-sieve oxygen concentrators have largely replaced compressed gas cylinders in the supply of oxygen to invalids at their homes. Such concentrators preferentially adsorb nitrogen from air pumped under pressure during an adsorption period into one column containing a bed of molecular sieve particles. The oxygen, with other non-adsorbed components, passes into a product reservoir from which it is dispensed to the user. When the sieve material in the first column becomes saturated with nitrogen, the feed air is switched to the second column where the adsorption is repeated. Upon switching, the first column is vented to the atmosphere, and adsorbed nitrogen flows out of the sieve material and may be swept from the bed by an addition of oxygen-enriched gas during a purge period. After purging, the first column is ready for a subsequent adsorption period.
The length of time for cycling the columns is usually set so that switching occurs just before the adsorbing column becomes saturated with nitrogen. Since adsorbents commonly become fouled over long use, cycle time is initially set conservatively (shorter than necessary), as is the peak pressure of the adsorption period (lower than optimum). Commonly, cycle time is controlled by a timer; is the same for each column; and does not change as sieve capacity decreases. This results in sub-optimum efficiency over the life of the columns since, initially, the adsorption capacity of the sieves is not fully utilized, and finally, unchanging cycle time allows nitrogen break-through as sieve capacity decreases.
Prior dual-sieve concentrators have attempted to increase efficiency by varying the cycle period in response to product use rate (U.S. Pat. Nos. 4,561,287, 5,042,994) and purity (U.S. Pat. No. 4,857,086). Some concentrators also use timers to control purge (U.S. Pat. Nos. 4,449,990, 4,545,790) and product release (U.S. Pat. No. 5,002,591). However, no prior dual-sieve oxygen concentrator known to applicant independently varies the cycling period of each sieve column and, therefore, loses efficiency when the adsorption capacity of one sieve differs from the other. Nor does any prior oxygen concentrator known to applicant provide purge and product release coordinated with a variable cycling period.